Integrated circuits (“ICs”) are incorporated into many electronic devices. IC packaging has evolved, such that multiple ICs may be vertically stacked in so-called three-dimensional (“3D”) packages in order to save horizontal area on a printed circuit board (“PCB”). An alternative packaging technique, referred to as a 2.5D package may use an interposer, which may be formed from a semiconductor material such as silicon, for coupling one or more dies to a substrate. A plurality of IC chips, which may be of heterogeneous technologies, are mounted on the interposer. Connections among the various ICs are routed through conductive patterns in the interposer. These interposer and stacked IC techniques are called 2.5D-IC and 3D-IC, respectively.
Electromigration (EM) decreases the reliability of integrated circuits, and eventually may cause degradation or failure of a semiconductor device. EM is caused by transfer of conductive materials through diffusion of ions or atoms. This phenomenon becomes more important in stacked ICs such as 3D-IC when the interconnect width decreases to hundreds or tens of nanometers.